In an image display device in which a fluorescent screen is scanned by an excitation light to display an image, the relative positional relationship between the scanning system and the fluorescent screen typically changes due to various causes such as vibration, distortion, or changes in the environment such as temperature or humidity, the influence of gravity, or changes over the passage of years, whereby the appropriate irradiation beam timing becomes difficult to maintain and image quality deteriorates.
In Patent Documents 1 and 2, image display devices are described that include: a fluorescent screen; an optical module that scans the fluorescent screen with a laser beam (excitation light); an optical sensor that detects the excitation light (feedback light) that is reflected by a reflection means on the fluorescent screen and generates a monitor signal for detecting the position of the laser beam on the fluorescent screen; and a feedback control unit that, based on the monitor signal from this optical sensor, controls the ON/OFF timing (light emission timing) of the laser beam in the optical module. The fluorescent screen includes a plurality of phosphor stripes and a reflection means that is provided between each of the phosphor stripes.
In the above-described image display device, an image is displayed by scanning the fluorescent screen in a direction orthogonal to the phosphor stripes by an excitation light beam (optical pulse) that is modulated based on a modulated signal to excite the phosphor of each phosphor stripe. In the feedback control, while carrying out this image display, a delay process is carried out on the modulated signal such that the position of each optical pulse moves back and forth in the scanning direction on the fluorescent screen. By means of this delay process, the output value of the optical sensor changes in accordance with the position of the beam with respect to each phosphor stripe. The optimum light emission timing is obtained based on the change in output of this optical sensor.